The Antarctic ice shelf break is good news for ocean dwellers

The Antarctic ice shelf break is good news for ocean dwellersJuly 20, 2017

An ice slab the size of Delaware broke off the Antarctic peninsula last week. This was no surprise to scientists: a crack in the ice shelf had been expanding over the past few months, eventually zigzagging 18 miles long and 300 feet wide.

This might not look so good, given the looming threat of global warming in the region. However, the ice shelf’s departure is good news for organisms on the ocean floor. “The ocean floor under an ice shelf is in total darkness, so there’s no photosynthesis, no plankton,” said Dave DeMaster, Ph.D. “It’s a biological desert.”

As ice shelves—which extend over the ocean—detach and float away, the ocean floor beneath will experience the sun’s rays for the first time in hundreds, if not thousands of years. The shelf is at least 700 feet thick in some places, and it cast an impenetrable shadow on the ocean floor. And after it departs, an ecological awakening happens.

“We go from biological desert to biological oasis,” said DeMaster.

The water under the ice shelf is chock full of nutrients like nitrogen and phosphorous. The ocean floor supplies these nutrients, and the freezing and melting of sea ice keep the nutrients circulating to the surface.

Add sunlight to nutrient-rich water, and soon phytoplankton, or algae, are thriving. Algae are the ocean’s primary producers: they photosynthesize, converting sunlight into energy and becoming food for other organisms. According to DeMaster, algae attracts more diversity, and soon krill move in, followed by sea cucumbers and sea worms.

DeMaster said that because of the nutrient-dense water and the sudden availability of sunlight, these bottom-dwelling organisms are able to create a food bank and sustain themselves through the winter.

Meanwhile, the ice shelf may continue to break apart as it floats. The ice slab was a 12 percent chunk of Larsen C, a massive glacier spanning both land and sea.

Ice shelves often break free, or “calve,” in the Antarctic's western peninsula, but this shelf is the second largest ever recorded. Fortunately, the shelf won’t contribute to sea level rise since it’s already floating. But without the shelf holding back the rest of the ice sheet, there’s nothing stopping the land-portion of Larsen C to slip into the water and raise sea levels.

Although it’s too soon to specifically blame climate change, the ice shelf was the third to break from the Antarctic peninsula in the last two decades.

“Calving is definitely natural but this much having calved is unusual, at least in the last 120 years we’ve been studying the Antarctic,” said DeMaster.

DeMaster says this much calving indicates more instability in the Antarctic's western peninsula.

While ocean life diversity may profit from these significant movements, only time will tell what they mean for the rest of the Antarctic region and beyond.

- Rossie Izlar

Rossie Izlar is the associate producer of Sci Tech Now North Carolina, a weekly show highlighting the latest science stories from North Carolina and across the nation.